Liquid crystal display devices have a liquid crystal cell in which nematic liquid crystals are filled between a pair of glass substrates. According to an operating mode of the liquid crystal cell, the liquid crystal devices are classified into TN (Twisted Nematic) mode, VA (Vertical Alignment) mode, IPS (In-Plane Switching) mode, OCB (Optically Compensatory Bend) mode, ECB (Electrically Controlled Birefringence) mode and so forth. While these operating modes differ in details such as an alignment direction of liquid crystal molecules, they are the same in function that electrically controls quantity of light passing through the liquid crystals and thereby displays characters and images.
Able to provide excellent contrast ratio when viewed from the front, the VA mode liquid crystal display devices are favored these days. The VA mode liquid crystal display device has a liquid crystal layer whose liquid crystal molecules are vertically aligned to the glass substrates that hold the liquid crystal layer. Disposed outside the glass substrates is a pair of polarizing plates in crossed nicols arrangement. When no voltage is applied, linearly polarized light that passed through the polarizing plate on a light incoming side (polarizer) goes through the liquid crystal layer with its polarization plane substantially unchanged. This light is subsequently blocked by the polarizing plate on a light outgoing side (analyzer), and a black display state is created. When the maximum voltage is applied, the liquid crystal molecules shift the alignment direction to parallel to the glass substrates. Linearly polarized light that passed through the polarizer changes its polarization plane at 90 degrees as it goes through the liquid crystal layer. This light passes through the analyzer, and a white display state is created.
Generally, the VA mode liquid crystal display devices have a problem related to the direction of viewing, or a viewing angle dependency problem, where they allow leakage of light at certain viewing angles and do not appear black in a black display state. Because of this drawback, the viewers at oblique angles possibly see poor contrast ratio or gray scale inversion where the gray levels are inverted. Thus, there is proposed an optical element for optically compensating retardation of light which suppresses a cause of the light leakage, induced by the liquid crystal layer (see, for example, the Japanese patent laid-open publication No. 2004-145268). This optical element has an optical anisotropic layer functioning as a C-plate whose optical axis extends along normal of the element substrate, and compensates the retardation of light that enters the VA mode liquid crystal cell at an oblique angle.
However, since liquid crystal molecules in the VA mode liquid crystal cell are not completely aligned vertical when no voltage is applied thereto, even the light that enters the glass substrate at a right angle is subject to the retardation. Because of the retardation, as shown in FIG. 7B, a peak position for the best contrast shifts in the alignment direction of the liquid crystal molecules. As a result, the contrast ratio of the image on the display screen is lowered.
In view of the foregoing, an object of the present invention is to provide a retardation compensation element able to compensate the optical retardation occurred in the VA mode liquid crystal cell, and to provide a liquid crystal display device and a liquid crystal projector equipped with this retardation compensation element.